Double-solenoid type electromagnetic valve provided with two solenoid mechanisms has been widely known in the past. In general, the electromagnetic valve of this type comprises a main valve unit having a spool type main valve disc to control main fluid, and a pilot valve unit to control pilot fluid, whereby the pilot valve unit is provided with two solenoid mechanisms, and these solenoid mechanisms are actuated alternately to control supply and discharge of the pilot fluid. By applying operating force of pilot fluid pressure alternately on both sides of the main valve disc, the main valve disc is switched over.
In the double-solenoid type electromagnetic valve as described above, two solenoid mechanisms are integrally molded to facilitate the operation by reducing the number of components as disclosed in Japanese Utility Model Laid-Open Publication 64-41778.
However, when two solenoid mechanisms are integrally molded, and if trouble occurs to one of the solenoids, it is not possible to replace only the solenoid in trouble, but the other solenoid not in trouble must also be abandoned. Because the solenoid mechanism occupies considerable percentage in the cost of the electromagnetic valve, economic loss due to the abandonment of the solenoids is extremely high.
As a double-solenoid type electromagnetic valve without such disadvantage, the one with two solenoids separately furnished is also known, and one of such examples is disclosed in Japanese Utility Model Laid-Open Publication 5-13009, which has been filed by the present applicant. In this valve, two solenoid mechanisms are mounted on a pilot valve body having a pilot supply valve seats to be opened and closed by these solenoids on upper surface and lower surface thereof in such manner that one of the solenoid mechanisms is positioned on upper surface and the other is positioned on lower surface. As a result, the pilot valve unit is extremely long in longitudinal direction compared with the main valve unit. This leads to a large size valve and also causes problems such as the restriction to the mounting condition of electromagnetic valve because the pilot valve unit is extensively projected upward and downward. Moreover, it is necessary to fix two solenoids and pilot valve body integrally by a plurality of bolts and then to fix it on the main valve unit by bolts. This means further trouble in assembling procedure and replacement of solenoids when trouble occurs. As the means to supply electric power to the two solenoids, electric wires are connected to terminals of the solenoids by means such as brazing or screw. This leads to troubles in operation and in replacement of the solenoids.
Further, according to Japanese Utility Model Laid-Open Publication 5-13009, in case solenoids are out of operation due to accident such as power suspension, two manual operators to match each of the solenoids are provided on upper surface of the valve body to switch over the main valve disc by manual operation, while these manual operators are aligned closer to each other in lateral direction of the valve body, and it often leads to erroneous operation because operator tends to switch over two manual operators and main valve disc in erroneous direction. Moreover, because the two manual operators are designed to switch over communication of passages where pilot fluid flows, it is difficult to adequately arrange the pilot passage when these are arranged in narrow space closer to each other, and the problems for designing and manufacture occur because the passages must be designed as bypass.